In response to the increasing seriousness of global environmental issues, energy issues and the like, a solar cell is attracting attention as clean electric energy-generating means with no concern over depletion. In a case in which a solar cell is used outdoors such as on the roof of a building, it is usual to use the solar cell in a solar cell module form.
Generally, the solar cell module is manufactured in the following order. First, a crystalline solar cell element (hereinafter, in some cases, also referred to as a power generation element or a cell) formed of polycrystalline silicon or monocrystalline silicon, or a thin film-type solar cell element obtained by forming an extremely thin (several micrometers) film of amorphous silicon or crystal silicon on a glass substrate or the like is manufactured. Next, in order to obtain a crystalline solar cell module, a protective sheet (a transparent surface protective member) for the solar cell module, an encapsulating material for solar cell, the crystalline solar cell element, an encapsulating material for solar cell, and a protective sheet (a back surface protective member) for the solar cell module are sequentially laminated.
Meanwhile, in order to obtain a thin film-based solar cell module, a thin film-type solar cell element, an encapsulating material for solar cell, and a protective sheet (a back surface protective member) for the solar cell module are sequentially laminated.
After that, the solar cell module is manufactured using a lamination method or the like in which the above-described laminate is suctioned in a vacuum, heated and pressed. The solar cell module manufactured in the above-described manner is weather resistant and is also suitable for outdoor use such as on the roof of a building.
An ethylene/vinyl acetate (EVA) copolymer film is widely used as an encapsulating material for solar cell due to its excellent transparency, flexibility, adhesiveness and the like. For example, Patent Document 1 discloses an encapsulating film which is made of an EVA composition including a crosslinking agent and trimellitate ester and is excellent in terms of both adhesiveness and film-forming properties. However, in a case in which the EVA composition is used as a configuration material of an encapsulating material for solar cell, there has been a concern that components such as acetic acid gas generated from the decomposition of EVA may adversely affect a solar cell element.
Meanwhile, the use of a polyolefin-based material, particularly a polyethylene-based material, as an encapsulating material for solar cell has been proposed due to its excellent insulating properties (for example, refer to Patent Document 2).
In addition, a resin composition for an encapsulating material for solar cell in which an ethylene/α-olefin copolymer, which is crosslinked within a relatively short period of time and thus has a sufficient adhering force and has excellent balance between stiffness and crosslinking characteristics, is used has also been proposed (for example, refer to Patent Document 3).